Modelling of 25 storey building with the specified properties using ETABS

1.

Aim: to model and analyze a 25-storey building with given specifications and to cross-check the parameters as per IS 1893 provisions.

Procedure:

• Open the ETABS software.
• Click the file menu and choose to create a new model option.
• After choosing a new model a dialogue box will appear as model initialization.

• Choose the built-in settings option and select the display units and codes.
• After model initialization select the grid and story inputs from the New model quick templates dialogue box.
• In this dialogue choose custom grid spacing and custom story datata which are used to provide the inputs specified above.
• Enter X grid data at a distance of 4 meters and Y grid data as 4 at a distance of 4 meters.

• Now edit the stories by using the user-defined storey input,26 storeys are incorporated ( plinth at 1.5 meters height+ 25 storey with 3-meter height each). Storey 1 has been labeled as the master storey and all above levels are labeled similarly to that.

• Select material properties under the defined tab.
• Define the materials of concrete M30 grade and steel of transverse reinforcement as 415 grade and longitudinal reinforcement as 500 grade.

• Select Section properties under the defined tab.
• Click on the frame section and create a new property as beam and input the values as 300X400mm.

• After the defined properties for the column as 800X800 and slab thickness ass 150mm

• Using the membrane property, a slab size of 150mm has been added to the list. Membrane property will help to consider only slab weights and floor weights in the analysis of structure while no stiffness component of flange advantage is considered during calculation.

• Now draw a column of size 800X800mm at the intersection of the horizontal and vertical grid and beams with a quick draw tool keeping all stories on.

• Beams drawn using the quick draw beam tool keeping all the stories on.

• Using the quick draw floors option, all the slabs have been modeled keeping"similar stories" ON.

• Select assign and click on joint select pinned support.
• Fix the pin supports at the base.

• Now define the load patterns: click on the define ta and click on load patterns.
• Define the loads like dead load, live load, brick load, and earthquake load in the x direction and positive x and negative x and the same loads in the Y direction also. Mention IS codes of respective loads.

• Click on modify lateral load, set range from base to 25th storey and seismic zone factor as 0.36, importance factor 1.25, and time period 0.5 seconds.

• Do the same for all the earthquake loads.
• Assign the loads and select similar stories.
• Click on shell load under the assigned tab.
• Click on live load and give the value as 3kn/m^2.
• Click on apply.

• For the roof we will take only 50% of the live load.

• Similarly add live load of 10Kn/m^2 on all the beams.
• For that select all the beams from select object type beams.
• Goto the frame load and click on the distributed load and enter the value as 10 Kn/m^2.

• Now go to mass source from the define tab.
• Modify the mass source and tick mark the required loads.
• Add load patterns and assign to the model.

• Define the load cases:
• Click on the load combinations.
• Click on the add default design combos.

• Now create the diaphragm by going to the assigned tab then shell and select diaphragms.

• Click on ok.

• Analyze the model using analyze option then click on check model, the modeled structure is verified without errors and warnings.

• Using analyze>run analysis, the model is analyzed and deflection patterns and BMD/SFD patterns are cross-checked logically. It is understood that the worked model provides reliable results.

Results:

• The time periods and torsional for fundamental mode-1Y direction and fundamental Mode -1X direction is noted from the table and are as follows:

• so it is clear from the table that the torsional time period is less than the two translational time periods as required by IS 1893 provision table

CONCLUSION: The analysis is done and the result is within the range